Nuclear reactors

ABSTRACT

In a nuclear reactor fuelled with porous fuel and having a fluid coolant, the coolant enters the core axially and traverses the porous fuel in a radial sense before leaving the core in a continuing radial direction. Pressure drop between inlet and outlet passages is reduced by avoiding the need for the coolant to pick up axial momentum on leaving the fuel.

D United States Patent 1151 3,658 645 9 Hooper 1 Apr. 25, 1972 [541NUCLEAR REACTORS 3,275,521 9/1966 Schluderberg et al. ..176/59 x 72]Inventor: Alan Thomas Hooper, Weymouth, Dorset, 3'287910 11/1966 England3,368,946 2/l968 3,389,054 6/1968 [73] Assignee: United Kingdom AtomicEnergy Authority, 3,413,194 11/1968 London. England 3,420,738 1/1969[22] Filed 1969 FOREIGN PATENTS OR APPLICATIONS [21] 796350 1,041,17710/1958 Germany ..176/59 [30] Foreign Application Priority Data PrimaryExaminer-Carl D. Quarforth Assistant Examiner-Roger S. Gaither Feb. 7,1968 Great Britain ..6,170/68 Anomey LarSn Taylor and Hinds [52] U.S.Cl..176/61, 176/59, 176/64,

176/65, 176/66 1 ABSTRACT [51] Int. Cl ..G2lc [9/28, G21C 11/08, 621915/02 In a nuclear reactor fuelled i f l d h porous ue an av1ng a flu1d[58] Field of Search coolant, the coolant enters the core axially andtraverses the 76/64 87 porous fuel in a radial sense before leaving thecore in a con- 56 R flames Chad tinuing radial direction. Pressure dropbetween inlet and out- 1 e let passages is reduced by avoiding the needfor the coolant to UNITED STATES PATENTS pick up axial momentum onleaving the fuel. 3,322,643 5/1967 Sprague et a1. ..176/59 6 Claims, 4Drawing Figures r-- I I 'll 0 Q 0 I .0 0 Q Patented April 25, 1972BACKGROUND OF INVENTION This invention relates to nuclear reactorsemploying fluid permeable fuel, herein referred to as porous fuel.Proposals have been made hitherto for the use of porous fuel in nuclearreactor cores with the aim of improving the heat transfer between fueland coolant but, in general, these proposals were made for employingelongated porous fuel elements in reactor coolant channels of more orless conventional form, that is to say, within axially extendingchannels passing coolant in a generally axial direction with eithercoaxial or re-entrant flow.

SUMMARY OF INVENTION Accordingto the present invention in one aspect,there is provided a nuclear reactor havinga core boundary, within whicha critical mass of nuclear fuel-bearing material is supported in theform of porous walled, hollow, bodies spaced apart to define contiguousinterspaces between them, coolant inlet and outlet means traversing theboundary of the core so as to leave at least one unobstructed end faceof the core boundary for replacement of the fuel bodies, the coolantfollowing a flow path within the core between the interspaces and thehollow interiors of said bodies which flow path traverses the porouswalls.

Preferably the coolant flow path in the core is axial into the openend(s) of tubular fuel-bearing bodies and then radially with respect tothe core axis through the tube wall and through the contiguousinterspaces. 7

DESCRIPTION OF THE DRAWINGS One form of gas cooled nuclear reactorembodying the invention will now be described with reference to theaccompanying diagrammatic drawing in which:

FIG. 1 is an axial cross section through reactor core and its associatedheat exchangers;

FIG. 2 shows a plan view of a sector of the reactor of FIG. 1; FIGS. 3aand 3b show a typical tubular fuel element in respectively axial crosssection and cross section normal to its axis.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the accompanyingdrawing, the reactor core 1 is of right cylindrical shape with the axisX-X vertical, and this is circumscribed by an annular heat exchanger 2.Within the boundary of the core 1, a central fissile region 3, whichcontains fissile fuel sufficient for criticality, has axial blanketregions 4, 5 and an annular blanket region 6. Between the annularblanket region 6 and the heat exchanger 2, an annular neutron shield 7is provided. The heat exchanger 2 is designed for radial fiow andcomprises segment-shaped pipe runs of serpentine tube each run providingsuccessively superheater, boiler and economizer tube lengths. Provisionmay be made for reheat if necessary.

As shown also in FIG. 2, the regions 3 and 6 of the core 1 are occupiedby fuel bearing tubes 10, supported, axes parallel, on a regulartriangular lattice and spaced apart so as to leave intermediatecontiguous spaces 11. The tubes 10 of regions 3, 4 and 5, 6 are all openat their lower ends and closed at the top. Each has a porous side wallso that coolant entering the bore of the tube at the bottom end isallowed to permeate through the wall into the intermediate spaces 11 andthen to pass radially outwards towards, and through, the heat exchangers2. An example of tube construction is shown in FIGS. 3a, 3b in which itwill be seen that the tube has a porous wall formed of an inner skin 10aof stainless steel mesh and an outer skin 10b of porous ceramicmaterial, the intermediate space being fitted with a porous mass offission product retaining nuclear fuel particles. The fissile region 3,the upper and lower axial blanket regions 4, 5 and the radial blanketregion 6 of the core are comprised of such tubes whose hollow walls arefilled with porous masses of the appropriate nuclear fuel i 5 and forthe fissile core region may'bepacked into discrete axial lengths of thesame tube or separate tubes may be employed in superposition for eachkind of fuel. The outermost rows of tubes 7 which act as neutronshielding between the core and the heat exchanger 2 may be of anysuitable construction which meets this end.

For example they may consist of steel and water, in which case the steelmay be in the form of concentric tubes while the water would bemaintained under pressure and pass in a closed circuit to theexternallysituated cooler 70 and back to the shield tubes. It would be necessaryto provide a heat insulating layer, say of ceramic on the outside of theshield tubes to prevent excessive loading of the shield heat removingcircuit and the degrading of the main coolant circuit temperature beforeit reaches the heat exchanger 2.

In operation the lowerends of the bores of the porous walled tubes incore regions 3, 4, 5, 6 communicate with gas coolant manifold 12 beneaththe core to which gas is supplied by circulators as at 14, into thebores. Gas passes axially into the bores and percolates through the tubewalls where it becomes heated and emerges into the intervening spacesll. The gas flow in the spaces 11 is generally radial, and it then flowsbetween the shield tubes 7 and over the bank of heat exchanger tubes 2where the gas gives up its heat to a secondary coolant passed throughthe tubes 2. Thence the coolant passes through a gas plenum chamber 211through the circulator back into inlet gas manifold 12.

The gas inlet and outlet means being inclined to one another a face 13is left unobstructed and is available for refuelling and control gearetc. High temperature coolant is entirely contained within the core,blanket, shield, heat exchanger complex and only coolant at its bottomtemperature can be contiguous with the walls of the reactor pressurevessel (not shown).

In the example described the tubes 10 are said to be disposed on aregular lattice and while this is preferable from the points of view ofgood physics performance and of fuel handling convenience, advantage maybe gained by pitching the tube centres on an irregular or unevenlattice.

In a modified form of fuel bearing tube 10 the outer porous sleeve 10bobtains its porosity from one, or a number of holes through its wall.

In a further alternative the fuel bearing region of each or at leastsome of the tubes 10 is arranged in a number of coaxial annular regionsheld in position with annular interspaces between them.

Iclaim:

l. A nuclear reactor having a core comprising fuel bearing bodies in theform of a plurality of porous walled tubes spaced apart with their axesparallel, means for passing a coolant from one end of the core inparallel flow paths through the central bores of the tubes and thenradially outwardly through the porous walls of the tubes, thearrangement being such that the outlet coolant flow path from the tubewalls to the core periphery lies in a direction normal to the axes ofthe tubes with none of the coolant exiting through the other end of thecore, and means for withdrawing coolant from the core in said direction.

2. A nuclear reactor as claimed in claim 1 including one or more annularrows of fertile fuel bearing fuel elements disposed about the peripheryof the core.

3. A nuclear reactor as claimed in claim 1 in which a number of heatexchanger tubes carrying secondary coolant are disposed about theperiphery of the core.

4. A nuclear reactor as claimed in claim 3 in which the out flow ofcoolant from between the heat exchanger tubes is directed back into thebores of the porous walled tubes via a flow path external to the core.

jacent the lower end wall boundary, a heat exchanger surrounding thecore, means for passing a coolant in flow paths within the tube boresand radially outwardly through the porous walls of the tubes to the heatexchanger and thence back to the coolant inlet plenum with none of thecoolant exiting through the upper end wall boundary, and a facilityadjacent the upper end wall boundary for refuelling the core.

1. A nuclear reactor having a core comprising fuel bearing bodies in theform of a plurality of poRous walled tubes spaced apart with their axesparallel, means for passing a coolant from one end of the core inparallel flow paths through the central bores of the tubes and thenradially outwardly through the porous walls of the tubes, thearrangement being such that the outlet coolant flow path from the tubewalls to the core periphery lies in a direction normal to the axes ofthe tubes with none of the coolant exiting through the other end of thecore, and means for withdrawing coolant from the core in said direction.2. A nuclear reactor as claimed in claim 1 including one or more annularrows of fertile fuel bearing fuel elements disposed about the peripheryof the core.
 3. A nuclear reactor as claimed in claim 1 in which anumber of heat exchanger tubes carrying secondary coolant are disposedabout the periphery of the core.
 4. A nuclear reactor as claimed inclaim 3 in which the out flow of coolant from between the heat exchangertubes is directed back into the bores of the porous walled tubes via aflow path external to the core.
 5. A nuclear reactor as claimed in claim3 in which a number of water cooled shield tubes are disposed betweenthe heat exchanger tubes and the periphery of the core.
 6. A nuclearreactor comprising a right cylindrical core arranged with its axisvertical and having upper and lower end wall boundaries, the core beingcomposed of a plurality of fuel bearing porous walled tubes arrangedwith axes parallel and parallel to that of the core, the tubes havingopen lower ends communicating with an inlet coolant plenum chamberadjacent the lower end wall boundary, a heat exchanger surrounding thecore, means for passing a coolant in flow paths within the tube boresand radially outwardly through the porous walls of the tubes to the heatexchanger and thence back to the coolant inlet plenum with none of thecoolant exiting through the upper end wall boundary, and a facilityadjacent the upper end wall boundary for refuelling the core.